The invention concerns an NMR (nuclear magnetic resonance) measuring system, comprising an NMR probehead in a vacuum housing, the NMR probehead being positioned inside an NMR magnet system during operation and containing a test sample and at least one NMR resonator that is cooled to cryogenic temperatures by means of a first cooling device, wherein the NMR resonator is thermally connected to a cooling head of the first cooling device via a heat conducting carrier element and via a first heat conducting connecting element.
An NMR measuring system of this type is disclosed e.g. in U.S. Pat. No. 5,889,456 (document [1]).
FIG. 2 schematically shows the prior art described in [1].
NMR spectroscopy has become a highly established technology, which is used for different applications such as e.g. MRI and high-resolution NMR spectroscopy on liquid samples. The signal-to-noise ratio (SNR) must have as large a value as possible in order to be able to utilize NMR technology in the first place. This is obtained i.a. with higher magnetic fields, with an optimum construction of the NMR resonators and, in particular, by cooling the NMR resonators and the associated NMR preamplifiers to cryogenic temperatures. Cryogenic liquids, e.g. liquid helium and/or liquid nitrogen and also active cooling devices are used for cooling.
Active cooling devices, however, are disadvantageous in that they operate with moving parts and therefore cause mechanical vibrations that must be optimally damped to prevent generation of excessively large sidebands in the NMR spectrum. The present patent proposes measures to achieve this object.
U.S. Pat. No. 5,889,456 [1] realizes cooling of the preamplifier or the NMR resonators with a complex separate cooling unit that cools the NMR resonators and the preamplifier via a heat exchanger using highly-cooled, compressed helium gas. The cooling devices used for this purpose are e.g. GM coldheads or pulse tubes. These cooling devices are disadvantageous due to the high maintenance and operating costs (electrical power>8 kW). The design of the heat exchangers also requires great effort.
U.S. Pat. No. 7,003,963 [2] describes the construction of an NMR probehead which is directly connected to a coldhead of a cooling device. This system does not require cryogenic liquids and gases outside of the cooling device, for which reason the construction of the overall system is very simple. Complex heat exchangers can be omitted and cooling power losses can be considerably limited. Moreover, the use of Free-Piston Stirling Coolers (FPSC) considerably improves the reliability of the cooling device.
However, due to direct coupling, the vibrations of the cooling device are directly transmitted to the NMR resonator, where they modulate the measured NMR signal. For this reason, strong sidebands are generated in the NMR spectrum. This is not admissible in high-resolution NMR.
In contrast thereto, it is the underlying purpose of the present invention to improve an NMR measuring system of the above-described type with as simple technical means as possible and in such a fashion that the sidebands in the NMR spectra are preferably minimized.